BMW is introducing its three cylinder engine to the public soon.
They discussed this last year in conjunction with the common engine architecture at their Innovation Day. So why go to three cylinders? Well there are a number of reasons, packaging, less friction, and emissions control among them.
In reality the three cylinder is not that different than an inline six, a ‘baby six’ if you will. And logically an inline six is merely two inline three cylinders. Like the six, the three cylinder has crankshaft throws at 120 degrees though there’s only one ignition event every 240 degrees of crankshaft rotation on the three.
The three cylinder will run well with a mono-scroll turbo (think how the N54 had one small turbos on each bank of three cylinders). The exhaust won’t sound funky either, like an inline five does. And the three cylinder should not be mistaken for a ‘three quarter four’, it is anything but.
The three cylinder configuration has a packaging advantage over a four cylinder in a transverse engined front wheel drive chassis. It is narrower (side to side) than a four cylinder and will allow for a narrower body or a tighter turning circle, if the manufacturer takes advantage of it.